Check out these other great tools:

Below are some links to some freely available corpus linguistics/NLP tools:

Coh-Metrix is an advanced natural language processing tool that analyses a number of textual features related to cohesion, lexical sophistication, syntactic complexity, and text difficulty. Check it out here.

VocabProfile is a great text analysis program with a free online interface. I find it to be particularly useful for quickly assessing learner text difficulty. The web interface is maintained﻿ by Tom Cobb and is based on the program Range, which was written by Heatley and Nation. Check it out here.